My fix for forcing retreat is to make it a one turn avert.
And the term for "flintlock arquebus" is "musket". This means that they do have flash powder and any chemist should be able to devise ninja style flash/smoke bombs.
This moves the gun timeline from 1400 to 1630, so expect to encounter a rifle eventually. (Accurate shot at 600 hexes.)
https://www.pbs.org/opb/historydetec.../gun-timeline/